Ion implantation is a process used in the manufacture of semiconductor devices. Typically, ionized dopants, such as A.sub.s H.sub.3 (arsine) and PH.sub.3 (phosphine), are implanted into the surface of a masked wafer by accelerating them at high speed. Once an ion is implanted, it can be diffused to desired regions of the semiconductor device. A typical ion implanter includes an ion source for producing ions, a beam line, and an end station. The beam line may include an analyzer for selecting specific ions, based upon their mass, from the ions generated by the ion source.
As illustrated in FIG. 1, a mass spectrometer may be used as an ion analyzer 18 to select specific ions. Supplied gas is turned to a plasma-state by the high-frequency voltage applied from the power source 12 in the ion source 10. Positive ions activated by the high frequency voltage are extracted, thus forming an ion beam 24. The ion beam 24 is focused via electric fields generated by voltage applied to a plurality of suppression electrodes 14 and ground electrodes 16 as illustrated.
The ion analyzer 18 selects the specific ions to be injected from the ion beam 24 by adjusting the electric field formed inside the ion analyzer chamber 19. The ion beam 24 is induced into the ion analyzer chamber 19 and ions within the ion beam are deflected at different angles within the ion analyzer chamber according to their mass. Most of the unwanted ions collide with the inner wall 50 of the ion analyzer chamber 19 and are extinguished. However, positive ions having the desired mass proceed through the ion analyzer chamber 19.
The positive ions induced into the inlet 20 of the ion analyzer chamber 19 are deflected by the electric field inside the chamber. The deflected angle of each positive ion in the ion beam is different according to each ion's intrinsic mass. The positive ions having a large mass have a small deflected angle, and the positive ions having a small mass have a large deflected angle. The positive ions which have deflected angles that are too large or too small collide with the inner wall 50 of the ion analyzer chamber 19, and are thereby extinguished. By contrast, the ions having the desired mass for injection pass through the ion analyzer chamber 19 and are extracted from the ion analyzer chamber at an outlet 22 located at the end of the ion analyzer chamber.
The ion beam of positive ions induced into the inlet 20 of the ion analyzer chamber 19 has a certain angle of dispersion. The ion beam of positive ions becomes more widely dispersed as it proceeds inside the chamber. Therefore, many of the positive ions collide with the inner wall 50 of the ion analyzer chamber 19. Unfortunately, a considerable number of ions having the desired mass are lost by the collisions caused by the ion beam dispersion angle. As a result, the current of the ion beam passing through the ion analyzer chamber may be weakened.
Another problem caused by the dispersion angle of the ion beam induced into the ion analyzer chamber 19 is that secondary electrons are generated as a result of these ion collisions. These secondary electrons have a polarity opposite to that of the positive ions within the ion beam. Accordingly, the secondary ions proceed in a direction opposite to the ion beam direction and interfere with the ion beam, further decreasing the current intensity of the ion beam.
The acceleration energy of an ion in ion implantation affects the depth of the ion when injected. The current intensity of an ion beam affects ion implantation processing time. Therefore, a reduction in ion beam current intensity because of collisions inside the inner wall 50 of the ion analyzer chamber 19, and because of secondary electrons generated thereby, may cause processing time delay during ion implantation.